Using an array of strings as model has the unfortunate effect that all
text nodes resulting from it are rebuilt whenever anything in the
array changes. Using a number as model only triggers a rebuild of
everything when the number changes.

Change-Id: I8a762e78eb75b282f46641a6cba6eff43c8ebfd5
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>